The disclosure relates to an illumination device of a microlithographic projection exposure apparatus, and to a microlithographic projection exposure method. In particular, the disclosure relates to an illumination device and to a microlithographic projection exposure method which, in conjunction with comparatively little structural outlay, enable a light property such as, e.g., the polarization or the intensity to be flexibly and rapidly changed or adapted.
Microlithography is employed for producing microstructured components such as integrated circuits or LCDs, for example. The microlithography process is typically carried out in a so-called projection exposure apparatus, having an illumination device and a projection objective. In this case, the image of a mask (=reticle) illuminated by means of the illumination device is projected, by means of the projection objective, onto a substrate (e.g., a silicon wafer) coated with a light-sensitive layer (e.g., photoresist) and arranged in the image plane of the projection objective, in order to transfer the mask structure to the light-sensitive coating of the substrate. During operation of a microlithographic projection exposure apparatus there is a need to set defined illumination settings, that is to say intensity distributions in a pupil plane of the illumination device, in a targeted manner. In addition to the use of diffractive optical elements (so-called DOEs), the use of mirror arrangements is also known for this purpose, e.g., from WO 2005/026843 A2. Such mirror arrangements include a multiplicity of micromirrors that can be set independently of one another.
Various further approaches are known for setting specific polarization distributions in a targeted manner, for the purpose of optimizing the imaging contrast, in particular in the pupil plane of the illumination device or in the reticle plane.
There can be a need to be able to set further different distributions of the polarization and/or intensity in the illumination device (that is to say different illumination settings). One application example thereof is, for instance, the compensation of polarization-dependent reflection properties of the HR layers present on the mirrors or AR layers present on the lenses, which, without compensation measures, have the effect that, e.g., elliptically polarized light is generated from originally linearly polarized light.
Furthermore, there is increasingly also a need to produce further illumination settings, which are sometimes also referred to as “freeform illumination settings” and which can have, e.g., a plurality of illumination poles in such a way that in some of said illumination poles the polarization direction is oriented perpendicularly (that is to say tangentially) and in others of said illumination poles the polarization direction is oriented parallel (that is to say radially) with respect to the radius directed at the optical system axis. Such illumination settings are used, e.g., in so-called “source mask optimization” in conjunction with comparatively exotic mask structures in order to obtain the desired structure by suitable combination of the mask design with the illumination setting during imaging at the wafer level.